Alloy steel



I 40 nitrogen content be at least thi v l I nitrogen as indicated bythese tests is most con- 40 Patented Feb. 1 2 1935 i I v UNITED STATES,PATENT OFFICE.

- ALLOY STEEL Russell Franks, Jackson Heights, N. Y., asslgnor toElectro Metallurgical Company, a corporatlon of West Virginia NoDrawing. Application July 29,1931,

- Serial No. 553,889

'1 Claims. (Cl. 15-1) My invention relates to chromium steels, reorhigher chromium content. The presence of ferring more specifically to ameans of improving other alloyed constituents in the steel, such as suchsteels, nickel, in no way limits or decreases the benefits It is theobject of my invention to improve to be derived from the use ofnitrogen. This 5 the physical properties of alloy steels containinginvention is therefore applicable to high ehroe 5 a high percentage ofchromium, and I attain 'miumsteels generally, is object by applying mydiscovery that the Experiments which I have made demonstrate addition ofnitrogen in alloying quantities apprethat the addition o nitrogen inamounts pp ciably greater than those normally present in ciably greaterthan those normally present in steels affects the physical properties ofhighsteels refines the grain-structure and improves l0 chromium steelsfavorably and to a marked dethe streng o h c m u st e s without gree.materially affecting their ductility, machinabil- It is a matter ofcommon observation and exty, a s corrosion resistance, or forging.perience that cast, high-chromium teels e nrolling and workingcharacteristics. For insist of oarse crystals and grains loosely boundstance, my tests show that the addition of about 15 together. Castingsof this metal are weak and to about 0.4% o alloyed nitrogen to actuallyporous, as shown by hydraulic tests at wrought and cast c r i m ls c naini high pressure. This coarse structure in cast r m abo t 8% t ab ut 3Ch omium and high-chromium steel is to a considerable extent 111) toabout 2% carbon g y improves the responsible for the comparatively poorphysical p y properties of these s e ls- The bene- 0 properties of themetal. A r fine ent of the ficial eiiect of the added nitrogen is mostmarked grainistructure is greatly to be desired for the in those steelscontaining less than about 1% production of steels with superiorphysical propf ar but n inu to e' ppr a le when erties. the carbon israised as high asabout 2%. i

to l have found that the presence of nitrogen In on s ri s f xper men sa number of in amounts greater than about 0.2% materially Wrought steeltest amples were made, each improves the physical properties of wroughtand sample comprising a preponderance of ir n. cast steels which containa large percentage of I about 0.1% of carbon, a u manga chromium.Although wrought chromium steels about 0.5% sil n a w percentage f impdo not, have the coarse grain-structure of the ties, and added Chromiumand nitrogene 30 cast metal, the application of my invention pronitrogenwas introduced into the molten steels duces marked improvements over thenormally in the form of Chromium nitride and a h good structure of thesesteels. My invention is t o ferro-ohlome' y- For e c hi thereforeapplicable not only to cast, but also to nit samp s a there wa p pa d awrought chromium steels, and produces a suo r spo d ng 10W nitrogen.steel having eDP 35 perior product in either case. mately the samecomposition in respect to every According to my invention, some benefitmay constituent except nitrogen. All of the samples be had by the use ofa nitrogen content somewere then Subje ed t a. number of p y a t stswhat less than 0.2%, but it is preferable that the under C p bConditions- T e ef ect of general, it is desirable to have the maximumveniently shown by means Of the fOHOWiIlg table: amount of nitrogenpresent that can be retained in stable combination at the temperatureswhich Analysis Physical properties are required for casting the metal.The amount of nitrogen which can be retained in the final %Cr %N Y 1 'r.s. El.% R.A.% Eric. Bxliiell 45 product increases with increasedchromium content; thus, a steel containing about 15% chro- 19 0.04 46 7730 7 5 m mium will retain up to approximately 0.2% 19 0.28 as 2o at 6:5nitrogen, while a steel containing about 35% 23 M3 47 68 31 52 7 5 12850 chromium .will retain up to approximately 0.65% 28 0.87 51 89. 26 67810 149 50 nitrogen 2o 0. cs 50 71 21 a9 7. 5 128 My invention isespecially valuable when ap- 26 83 24 45 128 plied to steels containingfrom about 15% to 35% of chromium, although it is of beneficial In theabove table of wrought steels, the foleflect when applied to steels ofsomewhat lower lowing symbols are used: Y. P. for yield point inthousands of pounds per square inch, T. S. for tensile strength inthousands of pounds per square inch. El. for percentage elongationobtainable in 2 inches, R. A. for percentage reduction in area of crosssection accompanying the elongation, Eric. for the values obtained usingthe Erichsen machine, and Brinell for the hardness values on the Brinellscale.

Amicroscopic examination of the wrought steels showed that nitrogengreatly refines the structure f the metal and appears to eliminate thegrain boundaries of the crystals. Further testing of the steelsdemonstrated that the addition of nitrogen decreases their tendency tobecome embrittled at elevated temperatures, such as those of the orderof 475 C.

A corresponding series of tests were made on cast high chromium steels.A series of castings containing a preponderance of iron, a lowpercentage of impurities, about 15% to 35% chromium, about 0.5% ofcarbon, and with high and low nitrogen contents, were cast in the formof stand ard arbitration bars and tested. Nitrogen was found to improvethe physical properties and refine the grain-structure greatly. Atypical set of values obtained from this series of tests follows:

Analysis Physical properties Or %N Doll. T.B.L. Brinell In the abovetable for cast steels, the following symbols are used: Defi. i'ordeflection in inches. T. B. L. for transverse breaking load in thousandsof pounds, and Brinell for the hardness values on the Brinell scale.

The presence of nitrogen in no way decreases the resistance of chromiumsteels to staining and certain types of corrosion, as I have determinedby extensive tests of both wrought and cast steels.

In making all castings used in my tests, 1 have followed a new andspecial procedure which I have developed for applying my invention. Alow carbon steel, according to my procedure, is melted in one of theusual types of furnaces. During the melting process the desired amountof nitrogen is introduced into the molten metal as chromium nitride or ahigh nitrogen ferrochrome alloy or other suitable nitride or mixture ofnitrides. After the steel is melted itis held at a temperaturesufiiciently above the melting point to allow the nitrogen liberatedfrom the unstable nitrides to escape. By regulating the temperature ofthe molten steel, the content of the combined stable nitrides can becontrolled to give solid cast metal, as the stability of the nitridesdecreases with a rise in temperature. This method of producing highnitrogen steels avoids the formation of blowholes and excessive piping,since the nitrogen remaining in the steel is in an alloyed condition.

Although I have described a number of specific examples and disclosedthe preferred form of my invention, it will be understood that these aremerely representative embodiments, and do not tend to limit the scope ofmy real discovery and invention relative to a method generallyapplicable to the improvement of alloy steels containing a high content01' chromium. I wish therefore to be limited only by the prior art andtile appended claims.

I claim:

1. An alloy steel comprising a preponderance of iron, about 15% to 35%chromium, about 0.10% to 2% carbon, and nitrogen in an amount not lessthan about 0.2% and not greater than about 0.65%, and the balancechiefly iron; said steel having throughout substantially the sameconcentration of nitrogen.

2. An alloy steel comprising a preponderance of iron, about 18% to 30%chromium, about 0.10% to 2% carbon, and nitrogen in an amount not lessthan about 0.2% and not greater than about 0.65%, and the balancechiefly iron; said steel having throughout substantially the same'concentration of nitrogen.

..,3. An alloy steel comprising a preponderance of iron'rfrom about 18%to about 30% chromium. from about 0.10% to about 1% carbon, and fromabout 0.2% to about 0.4% nitrogen, the balance chiefly iron; said steelhaving throughout substantially the same concentration of nitrogen.

4. Alloy steel comprising from about 18% to about 30% of chromium, fromabout 0.10% to about 1% of carbon, from about 0.2% to about 0.4% ofcombined nitrogen, and the balance substantially iron; said steel havingthroughout substantially the same concentration of nitrogen.

5. Fine-grained high-chromium iron-base alloy casting resistant tostaining, corrosion and high-temperature embrittling, and havingapproximately the composition: 15% to 35% of chromium, 0.10% to 2% ofcarbon, 0.20% to 0.40% of combined nitrogen, and the balancesubstantially iron; said casting having throughout substantially thesame concentration oi nitrogen.

6. An alloy steel consisting of about 15% to 35% chromium, about 0.10%to 1% carbon, about RUSSELL FRANKS.

